The invention relates to plastic pipe joining. More particularly, the invention relates to plastic pipe joining by mechanical clamps or couplers.
A well developed field exists in polymeric piping systems. Perhaps the most well known thermoplastic material for pipes and pipe fittings is polyvinyl chloride (PVC). PVC pipes and fittings are typically joined to each other via the use of a solvent cement to form joints characterized by solvent weld/bonds. Other solvent-weldable materials include chlorinated polyvinyl chloride (CPVC) and acrylonitrile butadiene styrene (ABS).
It may be less practical to solvent weld other thermoplastics such as polyethylene (PE, including high density polyethylene (HDPE) medium density polyethylene (MDPE), and low density polyethylene (LDPE)), polypropylene (PP), polystyrene (PS), polyamide (PA) and polybutylene (PB). Joining plastic pipe fittings by thermal welding (e.g., provided via butt-fusion or electrofusion) is an alternative to solvent welding.
In addition to such permanent joints, a number of other joints and configurations have been proposed. One family of joints involves bolted flanges wherein respective flanges are mounted at adjacent ends of adjacent pipe segments and secured to such pipe segments. Each flange has a hole circle for receiving a bolt circle coupling the two flanges together. A gasket may be sandwiched between the flanges for sealing.
Another family of mechanical joints involves a radial clamping/compression. A clamp body may surround adjacent end portions of the pipe segments and are sealed radially between the pipe and the clamp body.
Other coupling arrangements include bell-and-spigot arrangements. For example, in some such couplings, a bell body is mounted over and secured to the end portion of one pipe and, in turn, receives the adjacent portion of the other pipe with a radial gasket therebetween.
The various joint techniques suffer a number of problems. First, some are difficult. For example, it may take much effort to tighten down a bolt circle. Also, a bell-and-spigot joint may suffer from reliability issues. For example, failure to properly seat the gasket (e.g., the gasket becomes rolled during insertion) may produce leaks.
Additionally, such joints suffer from an inability to accommodate axial pipe contraction under pressure. The internal pressurization of a plastic pipe will cause both a radial expansion and an axial contraction. If the pipe is rigidly mounted (e.g., a bolted flange joint), this contraction will be only partial and place the pipe joint under tension, potentially damaging the joint or pipe or causing loss of sealing. Thus a rigid flange joint may be subject to leakage and breakage and a bell-and-spigot joint may be subject to disengagement/separation of the spigot from the bell.